This invention relates to a vehicle braking system for use in a vehicle such as an automobile.
A vehicle braking system including a pneumatic booster interposed between a brake pedal and a master cylinder and utilizing vacuum pressure in the intake manifold of an engine of the vehicle for augmenting the force applied on the brake pedal in actuating the master cylinder is known to the public. Typically, the pneumatic booster comprises a shell casing, a flexible diaphragm, a power piston connected to the diaphragm and defining a constant pressure (vacuum) chamber and a variable pressure chamber in the shell casing, an input shaft adapted to be connected to the brake pedal, a valve mechanism provided in the power piston and associated with the input shaft to control the pressure in the variable pressure chamber (to selectively connect or disconnect the variable pressure chamber with the vacuum chamber and atmospheric pressure), an output shaft adapted to be connected to a piston of a master cylinder and receiving the output force from the power piston, and a reaction mechanism for transmitting reaction force to the input shaft.
The reaction force is usually determined by the dimensional relationship between parts in the reaction mechanism, or by the so-called boost ratio of the booster.
While in braking the vehicle, it is preferable to control the deceleration changes in response to the depressing force applied on the brake pedal, however, when, for example, the weight of the vehicle is increased, the deceleration tends to decrease. Therefore, it is preferable to provide a braking system which makes it possible to adjust the output force of the pneumatic booster in response to various operational conditions of the vehicle.